In general, what is the status of gm2? I had thought it long-dead, until seeing this thread. Once upon a time I had written a fair amount of code in Modula-2, including the types of stuff that people generally thing can only be done in C. (Reentrant iterrupt handlers (in DOS, no less) and routines for reading and writing legacy binary data formats, to name two.)_________________.sigs waste space and bandwidth

I can clone the gnu pascal ebuild in order to do something similar
but imagine i want to add fortran (i suppose it is perfectly integrated in the gcc tree)
manually i can provide the configure statement languages=c,c++,fortran
exacly where emerge is telling the .configure to configure the build up in this way ?
if i open /usr/portage/dev-lang/gcc/* i can't fine nothing about it

Yes, it is encoded in the ebuild, but the actual functonality is hidden in the toolchain eclass. Take a look at gcc-compiler-configure () in /usr/portage/eclass/toolchain.eclass , there you'll find what you are looking for.